U.S. patent number 5,417,313 [Application Number 08/240,399] was granted by the patent office on 1995-05-23 for disc rotor for preventing squeal.
This patent grant is currently assigned to Akebno Brake Industry Co., Ltd., Akebono Research And Development Centre Ltd.. Invention is credited to Toshitaka Izumihara, Mikio Matsuzaki, Toru Yoshino.
United States Patent |
5,417,313 |
Matsuzaki , et al. |
May 23, 1995 |
Disc rotor for preventing squeal
Abstract
A hollow hole is radially formed in a rotor in at least one
position on its circumference so that the minimum thickness between
an inner surface of the hollow hole and each of the front and rear
braking surfaces is selected to be not larger than 3 mm.
Alternatively, in a ventilated rotor, at least one of a plurality
of holes formed radially in the rotor is shaped into an expanded
hole so that the minimum thickness between an inner surface of the
hole and each of the front and rear braking surfaces is selected to
be not larger than 3 mm. Two rows of small circular holes may be
formed in a specific arrangement so as to penetrate a disc rotor.
If longitudinal wave vibration is transmitted to the disc rotor,
squeals due to an even number order resonance mode, that is, a
resonance mode of the second, fourth, sixth order or the like, can
be effectively attenuated by specially shaped hollow holes, reduced
holes, or two rows of small circular holes formed in a disc
rotor.
Inventors: |
Matsuzaki; Mikio (Kasukabe,
JP), Izumihara; Toshitaka (Kitamoto, JP),
Yoshino; Toru (Gyoda, JP) |
Assignee: |
Akebno Brake Industry Co., Ltd.
(Tokyo, JP)
Akebono Research And Development Centre Ltd. (Hanyu,
JP)
|
Family
ID: |
16509237 |
Appl.
No.: |
08/240,399 |
Filed: |
May 10, 1994 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
915977 |
Jul 21, 1992 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Jul 23, 1991 [JP] |
|
|
3-205580 |
|
Current U.S.
Class: |
188/218XL;
188/264AA; 192/113.2 |
Current CPC
Class: |
F16D
65/0006 (20130101); F16D 65/12 (20130101); F16D
65/128 (20130101); F16D 2065/1308 (20130101); F16D
2065/1328 (20130101); F16D 2069/004 (20130101) |
Current International
Class: |
F16D
65/12 (20060101); F16D 65/00 (20060101); F16D
69/00 (20060101); F16D 065/12 () |
Field of
Search: |
;188/218A,218XL,264A,264AA ;192/113.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2083987 |
|
Dec 1971 |
|
FR |
|
2458048 |
|
Jun 1976 |
|
DE |
|
51-68985 |
|
May 1976 |
|
JP |
|
54-108880 |
|
Jul 1979 |
|
JP |
|
56-164236 |
|
Dec 1981 |
|
JP |
|
1114296 |
|
May 1968 |
|
GB |
|
2024966 |
|
Jan 1980 |
|
GB |
|
2125911 |
|
Mar 1984 |
|
GB |
|
2239685 |
|
Jul 1991 |
|
GB |
|
Primary Examiner: Oberleitner; Robert J.
Assistant Examiner: Rutherford; Kevin D.
Attorney, Agent or Firm: Cushman Darby & Cushman
Parent Case Text
This is a continuation of U.S. application No. 07/915,977, filed on
Jul. 21, 1992, which was abandoned.
Claims
What is claimed is:
1. A disc rotor arrangement for preventing squeal, comprising:
a ventilated rotor element having a plurality of holes extending
radially therein and being capable of passing air therethrough,
said rotor having a front braking surface and a rear braking
surface;
wherein at least one of said holes is an expanded hole expanded in
a direction toward said front and rear braking surfaces relative to
remaining ones of said plurality of holes, said at least one hole
radially passing through said rotor between said front and rear
braking surfaces, said expanded hole reducing a first minimum
thickness between an inner surface of said expanded hole and each
of said front and rear braking surfaces in an axial direction
relative to a second minimum thickness between an inner surface of
said remaining ones of said plurality of holes and each of said
front and rear braking surfaces in an axial direction.
2. A disc rotor arrangement for preventing squeal according to
claim 1, wherein said expanded hole is curved in cross sectional
area near each of said front and rear braking surfaces.
3. A disc rotor arrangement for preventing squeal according to
claim 1, wherein said first minimum thickness is not larger than
about 3 mm.
4. A disc rotor arrangement for preventing squeal according to
claim 1, including a plurality of said expanded holes.
5. A disc rotor arrangement for preventing squeal according to
claim 1, wherein said expanded hole has a cross section which
provides a variable thickness in said ventilated rotor element
between said expanded hole and each of said front and rear braking
surfaces.
6. A disc rotor arrangement for preventing squeal, comprising:
a ventilated rotor, said ventilated rotor having a radial outer
surface and a radial inner surface, said ventilated rotor having at
least one expanded hole and at least one unexpanded hole, each of
said expanded and unexpanded holes capable of having air flow
therethrough;
a front braking surface on said ventilated rotor, said front
braking surface having a radial width between said radial outer
surface and said radial inner surface; and
a rear breaking surface on said ventilated rotor, said rear braking
surface having a radial width between said radial outer surface and
said radial inner surface;
wherein said at least one expanded hole is formed to extend
radially in said ventilated rotor from said radial outer surface
toward said radial inner surface, said at least one expanded hole
reducing a first minimum thickness between an inner surface of said
at least one expanded hole and each of said front and rear braking
surfaces in an axial direction relative to a second minimum
thickness between an inner surface of said unexpanded hole and each
of said front and rear braking surfaces in an axial direction.
7. A disc rotor arrangement for preventing squeal according to
claim 6, wherein said at least one expanded hole is curved in cross
sectional area near each of said front and rear braking
surfaces.
8. A disc rotor arrangement for preventing squeal according to
claim 6, wherein said at least one expanded hole has a cross
sectional area which provides a variable thickness in said
ventilated rotor element between said inner surface of said at
least one expanded hole and each of said front and rear braking
surfaces.
9. A disc rotor arrangement for preventing squeal according to
claim 6, wherein said first minimum thickness is not larger than
about 3 mm.
10. A disc rotor arrangement for preventing squeal according to
claim 6, including a plurality of said expanded holes.
11. A disc rotor arrangement for preventing squeal according to
claim 6, including a plurality of said unexpanded holes.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a squeal preventing disc rotor for
effectively preventing a squeal from occurring when a disc brake is
operated.
In a disc brake in which a disc rotor rotating with an axle is
pressingly sandwiched between friction pads operated by oil
pressure or the like to perform braking, it is known that an
extremely uncomfortable high frequency sound called a brake squeal
is generated depending on the hardness of the disc rotor, the
affinity between the rotor and the friction pads, or the like, when
the disc rotor is pressingly sandwiched by the friction pads.
As a countermeasure to the generation of such a high frequency
sound, a metal annular member is fitted in a disc rotor at its
outer circumference as disclosed in Japanese Patent Unexamined
Publication No. Sho-56-164236, or a hole or a groove is formed in a
rotor at its braking surface so as to shift a resonant point as
disclosed in Japanese Utility Model Unexamined Publication No. Sho.
54-108880.
Recently, however, various kinds of materials have been used as
friction materials. For example, when a material in a group of
semi-metallic or non-asbestos is used as friction pads, it is
impossible to sufficiently suppress the squeal by means of the
countermeasure for suppressing vibrations as described above. In
order to investigate the cause, a brake test was actually performed
by use of friction of a group of semi-metallic or non-asbestos
materials. As a result, it was found that a squeal is caused mainly
due to a so-called longitudinal wave (a compressional wave) in
which the front and rear surfaces of a rotor vibrate in the
directions opposite to each other. FIG. 7 shows the direction of
wave transmission in the rotor disc at arrow 70. Arrows 72 and 74
show the directions of vibration, and nodal lines of vibration 76
are formed.
The fact was proved by the detection that the resonance point of a
longitudinal wave obtained in an excitation test for measuring a
vibration characteristic of a single rotor product as shown in FIG.
8 coincides with the frequency of a squeal in an actual car test
using pads of a group of non-asbestos as shown in FIG. 9. This
result applied to an actual car test using pads of a group of
semi-metallic material.
FIG. 8 shows a vibration (longitudinal wave) application test
result. Arrow 80 in FIG. 8 shows the direction of the longitudinal
wave transmission. In the graph of FIG. 8, the overplotted dark
areas at points 82, 84 and 86 are the Second mode resonance, the
Fourth mode resonance, and the Sixth mode resonance, respectively,
for the resonance point corresponding to squeal and resonance point
of longitudinal wave. FIG. 9 shows an actual car squeal test
result, showing background noise 90, noise (squeal) corresponding
to Second resonance mode of longitudinal wave 92, Fourth mode of
resonance 94, and the Sixth mode of resonance 96.
As a result of a further experiment in which friction pads of a
group of non-asbestos were pressingly fitted on each of disc rotors
which were different in diameter from each other and which were
used in four actual cars (cars A, B, C and D) respectively to
thereby investigate the frequency characteristics, the data shown
in FIG. 10 was obtained. Being apparent from FIG. 10, portions at
which noises are caused by longitudinal waves concentrate on
resonance modes formed in even number orders, that is, the second,
fourth, and sixth orders. This is because the frequencies in the
other even number order modes exceed the human audible range of
frequency to thereby cause no problem. The reason why noise is not
generated in any odd mode is that the odd number mode has no
resonance point because a disc or ring-like body such as a rotor
has no open end unlike a rod-like body having open ends so that
compressional waves circulating in the rotor solid body interfere
with each other to cancel the odd modes. FIG. 10 shows the
calculated frequency of the longitudinal waves of the sixth mode
106, the Fourth mode 104 and the Second mode 102 as a function of
the rotor outer diameter. FIG. 10 also shows a depiction of the
Second mode longitudinal waves 112 and the Fourth mode longitudinal
waves 114, as they travel around the disc rotor.
SUMMARY OF THE INVENTION
On the basis of the above, it is an object of the present invention
to effectively attenuate a brake squeal caused mainly by a
longitudinal wave as well as by a transverse wave, only by the
provision of a hollow hole or a hole of a special shape or two rows
of small circular holes of a special arrangement in at least one
circumferential portion of the braking surfaces of a disc
rotor.
In order to achieve the above object, in the solid rotor according
to the present invention, a hollow hole is formed in the rotor in
at least one position on its circumference so as to extend from the
radially outside toward the inside so that the minimum thickness
between the hollow hole and each of front and rear braking surfaces
is selected to be not larger than 3 mm. In the ventilated rotor, at
least one of plural holes formed radially in the rotor is shaped
into an expanded hole so that the minimum thickness between the
hole and each of front and rear braking surfaces is selected to be
not larger than 3 mm.
In another configuration of the present invention, in a disc rotor,
a first row of small circular holes respectively having centers on
any axis OX extending in a desired radial direction from a center
of the rotor, and having the same shape are formed so as to
penetrate front and rear braking surfaces, and a second row of
small circular holes respectively having centers on a second axis
parallel to the first axis are similarly formed so as to penetrate
the front and rear braking surfaces, the first and second rows of
small circular holes being formed so as to satisfy the conditions
of
where d' and r' represent a diameter and a radius of each of the
small circular holes in the first row, C' represents an intervals
between the small holes in the first row, d" represents a diameter
of each of the small circular holes in the second row, C"
represents an interval between the small holes in the second row,
and represents the shortest distance between the first axis and the
small circular holes in the second row.
When the friction pads pressingly sandwich the braking surfaces of
the disc rotor so as to perform a braking operation, it is possible
to effectively attenuate a brake squeal caused mainly by a
longitudinal wave as well as by a transverse wave by a hollow hole
or a cooling hole of a special shape or two rows of small circular
holes of a special arrangement formed in at least one
circumferential portion of the braking surfaces of the disc
rotor.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIGS. 1A and 1B are views showing an embodiment of the present
invention in the case where the disc rotor is a solid rotor, in
which FIG. 1A is a plan view of the rotor, and FIG. 1B is a
partially broken side view of the rotor.
FIGS. 2A and 2B are views showing a second embodiment of the
present invention in the case where the disc rotor is a ventilated
rotor, in which FIG. 2A is a partially broken side view of the
rotor, and FIG. 2B is an enlarged view of a reduction hole.
FIG. 3 is a brake test result table showing the relationship
between the squeal coefficient and the thickness h'(h") of the
portion of a braking surface in which holes are formed.
FIGS. 4A, 4B and 4C are view showing a third embodiment of the
present invention in which small circular hole groups in two rows
are formed in a disc rotor, in which FIG. 4A is a plan view of a
rotor, FIG. 4B is a partially broken side view of the rotor, and
FIG. 4C is an enlarged view of small circular hole groups in two
rows.
FIG. 5 is a brake test result table showing the relationship
between the squeal coefficient and the arrangement of the two rows
of small circular holes.
FIG. 6 is a graph for comparing the differences in squeal between
the product according to the present invention and the conventional
one.
FIG. 7 is a view of analysis on vibrations of the disc rotor due to
longitudinal waves.
FIG. 8 is a view of analysis on vibrations onto a disc rotor by
longitudinal waves.
FIG. 9 shows the results of an actual car test using non-asbestos
pads.
FIG. 10 is a frequency characteristic data table experimentally
obtained by use of four disc rotors which were different in
diameter and which were actually used on cars.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1A and 1B show a first embodiment of the present invention in
the case where a disc rotor is a solid rotor. A hollow hole 11 is
formed in a solid rotor 10 in at least one circumferential portion
of the disc and formed radially from the outside toward the inside.
The sectional shape of the hollow hole 11 may be not only circular
but square, rectangular, or oval.
FIGS. 2A and 2B show a second embodiment of the present invention
where a disc rotor is a ventilated rotor, in which FIG. 2A is a
sectional view of a rotor and FIG. 2B is an enlarged view of a
reduction hole 22. At least one of a plurality of cooling holes 21
provided radially in the ventilated rotor 20 for passing cooling
air therethrough is subjected to reduction work so as to form a
reduction hole 22 partially enlarged in its inner hole portion
(hereinafter referred to as a reduction hole.)
The minimum thickness of each of the braking surfaces 12A and 12B
of the rotor which remain after the hollow holes 11 are formed are
represented by h' in the first embodiment, and, on the other hand,
the minimum thickness h" of each of the braking surfaces 23A and
23B of the rotor which remain after the reduction hole 22 is formed
is represented by h" in the second embodiment. A test was performed
to measure the generation of resonant frequencies and the degree of
braking squeal while changing the thicknesses h' and h".
Here, the generation of resonant frequencies and the degree of
braking squeal were numerically defined as a squeal coefficient
N.sub.P, which is an accumulation of a sound pressure (.mu.br)
converted from a sound pressure level (dB) representing the degree
of noise due to a squeal generated in one test.
Accordingly, the squeal coefficient N.sub.P is expressed by
##EQU1##
Where, N, Pi, and n represent the number of times of braking, a
sound pressure (.mu.br) of a squeal, and the number of times of
generation of the noises, respectively.
FIG. 3 is a table showing the results of a brake test showing the
degree of the squeal coefficient when the thickness h' or h" was
changed. The results of the test show that the squeal coefficient
becomes large in a range in which the thickness h' (h") exceeds 3
mm, and that there is no substantial effect for preventing a squeal
when the thickness h' (h") increases beyond 3 mm.
FIG. 4A shows a third embodiment in which two rows of small
circular holes are formed in one circumferential portion of a disc
rotor so as to extend in the radial direction, FIG. 4B is a
partially broken side view of the disc rotor, and FIG. 4C is an
enlarged view showing the two rows of small circular holes.
A first row of small circular holes (31Aa, 31Ab, 31Ac, 31Ad) and a
second row of small circular holes (31Ba, 31Bb, 31Bc) are formed in
the disc rotor 30 so as to be arranged in parallel to each other.
Each of the small circular holes penetrates to the front and rear
braking surfaces 32A and 32B.
The small circular holes (31Aa, 31Ab, 31Ac, and 31Ad) in the first
row respectively have circular sections having radii equal to each
other and having centers on a first axis OX extending in a desired
radial direction from the center of the rotor. The small circular
holes (31Ba, 31Bb, and 31Bc) in the second row respectively have
circular sections having radii equal to each other and having
centers on a second axis O'X' parallel to the first axis OX.
Assuming that the diameter and radius of each of the small circular
holes in the first row are represented by d' and r'; the interval
between the small circular holes in the first row is represented by
C'; the diameter of each of the small circular holes in the second
row is represented by d"; the interval between the small circular
holes in the second row is represented by C"; and the shortest
distance between the first axis OX and the small circular holes in
the second row is represented by r, it was then found from a result
of the brake test that a squeal was prevented effectively when the
conditions of d'>C", d">C', and r'-r.gtoreq.0 were satisfied.
FIG. 5 shows the results of the brake test at that time, and shows
the relationship among C", C', d", d', r'-r, and the squeal
coefficient. When r'-r was -2 or -1.5, the squeal coefficient was
large (in the range B) even if d' was larger than C". When d' was
equal to or smaller than C", the squeal coefficient was also large
(in the range C) even if r'-r was 1. However, the squeal was
effectively reduced in the range A where d'>C", d">C', and
r'-r.gtoreq.0 (in the range a).
If the longitudinal wave vibration is mainly transmitted to the
disc rotor, squeals due to an even number order resonance mode,
that is, a resonance mode of the second, fourth, sixth order or the
like, can be effectively attenuated by specially shaped hollow
holes, reduced holes, or two rows of small circular holes formed in
a disc rotor. Accordingly, it is possible to use various kinds of
friction pads selectively. FIG. 6 is a graph comparatively showing
the effects of the product according to the present invention and
the conventional one. It is found that squeals can be effectively
suppressed by the product according to the present invention even
in the case of using friction pads made of any material of a
semi-metallic group or a non-asbestos group. Further, it is
possible to provide a hollow hole, a reduction hole, or two rows of
small circular holes in accordance with the type of a rotor, and
those holes may be merely formed in at least one portion on the
circumference of the rotor. Accordingly, manufacturing time is
greatly reduced.
* * * * *